You can get cloth by the yard for like 1.99 if you buy cheap stuff at walmart. Spend 20$, buy 10 yards of cloth and rip it into strips and stuff the bag with that. If you want to be hardcore you can cut the legs off of a few pairs of old bluejeans (2-3$ at goodwill) and roll those up and put them in the middle to make a more solid core. Just make sure you have plenty of cloth around the jeans since denim makes a pretty solid wad when you roll it up tight. Oh, once it's rolled up put some heavy rubber bands around it to keep it that way. But really, cloth strips will probably do you fine.

lower end commercial bags are frequently filled with a core of sand surrounded by shredded cloth (about 1:2 by weight); however, over time this invariably results in broken sandbags and sand collecting in the bottom of the bag. you DO NOT want this. a good bag should be pretty consistent top to bottom; variation will lead to bad habits.

packed sawdust is HEAVY and HARD. be aware of this. most sawdust/sand filled bags i've seen have a foam liner so you don't break your damn leg on them.

my plan for my next heavy bag is rubber mulch; i believe it'll be fairly suitable in terms of weight and hardness without a liner. the downside is that it's about $.80/lb. i'm going to investigate it a bit more in the spring.

the bag we use most at my dojo, by the way, is a 42" ringside canvas bag filled with the cloth shreds (but not the sand) from an expired everlast of the same size. this results in a bag weighing 54lbs that is suitable (in terms of hardness) for bareknuckle work. as the cloth settles, i'm going to add more.

While you guys were posting all this useful information, I was filling my bag with alternating layers of wood chips (actual chips of wood, not saw dust) and old jeans. The finished product (until next week when I add more cloth) can be found here: www.greeleykyokushin.com/bag.jpg

Thanks again for all the advice, and hopefully I didn't ruin the bag. I can always remove the filling and try again right?

That's going to be a hard and possibly painful bag to kick... Hope it works out for you. I would have ditched the wood chips and put at least a layer of pillow cases or something around the jeans.... But I'm a wuss.

I'm invisioning a 2"x2" piece of wood as a "wood chip" are they smaller than that? I'm wondering what will happen if one of those makes its way near the surface of the bag and you catch a corner with your shin or something....

wood chips are pretty small, not big enough to do damage to the user or bag, but bigger then saw dust. Haven't you guys seen wood chips before?? Its the stuff you put on the floor of a horse stall or something.

The street argument is retarded. BJJ is so much overkill for the street that its ridiculous. Unless you're the idiot that picks a fight with the high school wrestling team, barring knife or gun play, the opponent shouldn't make it past double leg + ground and pound - Osiris